Olefin polymerization catalysts are of great use in industry. Hence, there is interest in finding new catalyst systems, including catalyst activators that increase the commercial usefulness of the catalyst and allow the production of polymers having improved properties.
Catalysts for olefin polymerization are often based on metallocenes as catalyst precursors, which are activated either with the help of an alumoxane, or with an activator containing a non-coordinating anion.
EP 0 277 004 A1 is one of the first documents disclosing polymerization catalysts comprising a bis-cyclopentadienyl metallocene compound that is activated by reaction with a secondary, ionic component comprising a non-coordinating anion (NCA) and a counter-cation. The NCA is, on the one hand, capable of stabilizing the active cationic catalyst species, but on the other hand only weakly coordinates to the metal center and thus can be displaced by a monomer to be incorporated into the polymer chain. The activators disclosed are ion pairs of an ammonium or phosphonium cation and a borate anion as the NCA. The cations disclosed are alkyl and/or aryl ammonium or phosphonium species. EP 0 277 004 A1 states that the conjugate base of the activator cation may be a neutral component which stays in solution and which preferably does not coordinate to the metal cation. Therefore, it is suggested to use relatively bulky conjugate Lewis bases to avoid coordination to and, thus, interfering with the active catalyst.
WO 91/02012 discloses the polymerization of high Mw, narrow molecular weight distribution polyethylene using a metallocene/activator system, wherein the activator comprises an NCA and an ammonium cation.
M. A. Giardello, M. S. Eisen, Ch. L. Stern and T. J. Marks in J. Am. Chem. Soc., 1995, 117, 12114-12129, report on the preparation of cationic polymerization catalysts from metallocene compounds, using various types of activators, including methylalumoxane (MAO) and NCA/cation pairs. It is suggested that, although the main focus in activator choice is on the NCA, the choice of the amine in the activator cation may also be important, as certain amines could coordinate to the metallocene cation and, thus, diminish its catalytic activity. In accordance with this suggestion is another finding also reported in this article, which is that the presence of an exogenous amine base significantly depresses the Mw of the polymer product as well as the polymerization activity (see Examples 9 and 10 of Table 3, page 12124).
EP 0 630 910 A1 teaches the use of free Lewis bases to control the activity of olefin polymerization catalysts. Lewis bases can, if necessary, terminate the catalytic reaction completely. However, the termination is reversible upon addition of alumoxane. The system disclosed thus comprises a metallocene compound, a Lewis base and an alumoxane. EP 0 630 910 A1 indicates that the metallocene cation-Lewis base complex is inactive for olefin polymerization because the olefin is unable to compete with the Lewis base for the coordination site at the metal. The Lewis bases used are, among others, amines, ethers, or phosphines in combination with a cyclopentadienyl-fluorenyl metallocene.
Despite the earlier teachings in the art as reported above, several authors and patent applications teach the separate addition of an amine base to the system comprising the metallocene compound, the cation/NCA activator, and, optionally, an organoaluminum compound. See for example U.S. Pat. No. 5,817,590 and E. A. Sanginov, A. N. Panin, S. L. Saratovskikh, N. M. Bravaya, in Polymer Science, Series A (2006), 48(2), 99-106. None of these references, however, disclose altering comonomer incorporation.
U.S. Pat. No. 5,416,177 discloses the use of metallocene compounds typically 1:1 molar ratios combined with activators comprising tris(pentafluorophenyl)borane and at least one complexing compound, such as water, alcohols, mercaptans, silanols, and oximes, for the polymerization of olefins, in particular 1-hexene. Similar catalyst systems are disclosed in WO 2005/016980.
WO 01/62764, WO 01/68718, and WO 2004/005360 disclose co-catalysts for use in olefin polymerization, wherein the co-catalysts comprise a cation derived from an aromatic, nitrogen-containing Lewis base, such as pyrrole, imidazole, or indole, and NCAs, particularly borates.
WO 01/48035 relates to catalyst systems comprising an organometallic compound (preferably a metallocene), a Lewis base, a support, and an activator. The activator is an ion pair, the anion of which is a borate, such as tetrakis(pentafluorophenyl)borate. The cation is an ammonium cation, such as a trialkylammonium.
WO 03/035708 seeks to provide a cocatalyst component for use in combination with olefin polymerization catalyst precursors, particularly metallocenes that result in highly active polymerization catalysts with good storage stability. The cocatalysts disclosed are composed of an ammonium cation and a NCA, and are supported on a fine particle carrier.
“Metallocene/Borate-Catalyzed Copolymerization of 5-N,N-Diisopropylamino-1-pentene with 1-Hexene or 4-Methyl-1-pentene” Udo M. Stehling, Kevin M. Stein, David Fischer, and Robert M. Waymouth, Macromolecules 1999, 32, 14-20 indicates that certain amines, when used as comonomers, had the effect of inhibiting the rate of total monomer conversion.
“Olefin Copolymerization with Metallocene Catalysts. II. Kinetics, Cocatalyst, and Additives”, James C. W. Chien and Dawei He, Journal of Polymer Science: Part A Polymer Chemistry, Vol. 29, 1595-1601 (1991), John Wiley & Sons, Inc., discloses that the molecular weight of ethylene/propylene copolymer is slightly increased by addition of Lewis base modifier but at the expense of lowered catalytic activity and increase in ethylene content in the copolymer in an ethylene/propylene copolymerization catalyzed by ethylene bis(indenyl)-ZrCl2/methylaluminoxane.
“Effect of Co- and Non-Copolymerizable Lewis Bases in Propylene Polymerization with EtInd2ZrCl2/MAO”, M. L. Ferreira, P. G. Belelli, D. E. Damiani, Macromol. Chem. Phys., 2001, 202, 830-839 discloses that with noncopolymerizable Lewis bases, the activity and the molar mass of poly(propylene) are diminished.
U.S. Pat. No. 7,799,879 discloses an activator comprising a non-coordinating anion and a preferably cyclic cation, where the cation is represented by the formula (1) or (2): [R1R2R3AH]+ (1) or [RnAH]+ (2), wherein A is nitrogen or phosphorus.
Furthermore, combinations of activators have been described in U.S. Pat. Nos. 5,153,157 and 5,453,410, European publication EP 0 573 120 B1, and PCT publications WO 94/07928 and WO 95/14044. These documents all discuss the use of an alumoxane in combination with an ionizing activator.
U.S. Pat. No. 7,985,816 discloses trimethylammonium containing non-coordinating anion activators.
Other references of interest include: U.S. Pat. Nos. 7,794,917; 7,592,401; 7,524,447; 6,723,676; 7,553,917; and U.S. Patent Application Publication Nos. 2011/0076454; and 2010/0029873.
There is still a need in the art for new and improved catalyst systems for the polymerization of olefins, in order to achieve specific polymer properties, such as high melting point, high molecular weights, to increase conversion or comonomer incorporation, or to alter comonomer distribution without deteriorating the resulting polymer's properties.
It is therefore an object of the present invention to provide a process and a catalyst system for use in a process for the polymerization of olefins, especially ethylene, wherein the resulting polymers have good melting points and comonomer distribution. Ideally, such catalyst system should also exhibit high catalytic activity under commercial polymerization conditions.
In another embodiment, it is an object of the present invention to provide a process and a catalyst system for use in a process for the polymerization of olefins, especially ethylene, to make block copolymers.